The present invention relates to a rechargeable battery with a nonaqueous electrolyte, and more particularly to a rechargeable battery with a non-aqueous electrolyte, comprising a cathode composite containing an iron compound having a particular property as a cathode active material, an anode material of a lithium ion doped compound and a non-aqueous electrolyte obtained by dissolving a fluorine compound in a solvent mixture of ethylene carbonate with an ether solvent.
In recent years, a rechargeable lithium battery having a high energy density has attracted attention, which has led to proposals of various compounds as the cathode material and examination of properties of these compounds.
Rechargeable batteries containing, as the cathode active material, lamellar compounds of a transition metal chalcogenide, such as titanium disulfide or molybdenum disulfide, have hitherto been commercialized.
These lamellar compounds, however, have not developed into wide use.
This is because the potential that batteries made with use of the above material can discharge is so low that the energy density can hardly be enhanced, the amount of natural resources of the material is limited, and so forth.
On the other hand, when a metallic lithium is used as the negative electrode, there occurs a problem of a short cycle life of the battery due to the occurrence of dendrite formation, etc.
In order to solve this problem, alloys, carbonaceous materials, etc., have come to be used as the negative electrode material.
This, however, requires the use of a material having a high discharge voltage also on the side of the cathode because any improvement in the energy density of the battery as a whole cannot be attained without use of such a material, so that the development of a cathode active material comprising a metal oxide material has been put forward.
In general, rechargeable batteries wherein use is made of lithium are expected as a power source for portable electronic equipment, a high performance battery for a dispersed-type battery energy storage system of electric automobiles as means for alleviating environmental problems, etc.
In order to spread the rechargeable lithium battery as a practical battery in the above-described applications, the rechargeable lithium battery should satisfy the following requirements: (a) the safety is high; (b) the resource reserve of the material used should be so high that the cost is low; and (c) the cycle life is long.
However, when a lithium-cobalt composite oxide or other material having a high discharge voltage of which the development is presently put forward is used, an oxidative degradation of a solvent in the nonaqueous electrolyte often occurs in a region where the potential exceeds 4 V, so that there is a possibility that bursting of the battery or other unfavorable phenomenon will occur if the battery is overcharged.
Further, metals such as cobalt and lithium are expensive, and the reserve thereof is not abundant.
Further, regarding the service life as well, since composite oxides such as lithium-cobalt are a crystalline material, it is conceivable that there will occur a lowering in the service life of the battery due to the disintegration of crystals accompanying the incorporation and release of lithium ions.
The present inventors previously developed a rechargeable battery with a nonaqueous electrolyte comprising as a cathode active material an aniline-containing amorphous FeOOH produced by reacting iron oxychloride (FeOCl) with aniline and as an electrolyte a propylene carbonate containing lithium tetrafluoroborate (LiBF.sub.4) dissolved therein in a concentration of 1.0 mol/dm.sup.3.
In this battery, however, the degradation of the discharge capacity was observed even at a relatively early cycle.
The stability of the electrolyte is also a factor having an influence on the cycle life and is related also to the safety of the battery.
However, it was found that the above-described electrolyte has drawbacks such that the anions of LiBF.sub.4 as the solute were liable to be decomposed by water as an impurity.